My PCH, like many others, is "cooking" and I have used various heatsinks etc over it to no avail.

Finally I have measured it with two electronic and one IR thermometer, and its temperature was for example 71C-72C but HWinfo reported 94C+. This is a significant difference between measured temps and reported temps.

Either the PCH is broken or Hwinfo is getting it wrong. Is there anyone else out there that can verify what's happening?

That means the temperature reported by HWiNFO should be the internal PCH temperature (measured by a diode inside the chip) and you measured the external surface temperature. That could explain the difference.
Which mainboard is that?